1. Technical Field
This disclosure generally relates to assemblies for installation in a workpiece. The assemblies include expandable outer members and fasteners.
2. Description of the Related Art
Fastener assemblies are often used to interconnect a plurality of workpieces, such as a stack of plates or other structural members. Some conventional fastener assemblies have a bolt and a collar that cooperate to apply a clamp-up force to a multi-component workpiece (e.g., overlapping panels). To form a joint, a hole is drilled through the multi-component workpiece. A bolt is then inserted through the hole such that an end of the bolt protrudes outwardly from the workpiece. The workpiece is clamped between a head of the bolt and the collar. Unfortunately, these types of joints are susceptible to fatigue damage and have undesired electrical properties. Contaminates (e.g., moisture, chemicals, debris, and other foreign substances) can become lodged between faying surfaces of joints and between the workpiece and bolt resulting in impaired electrical performance, increased wear, and increased corrosion. Cyclic loading can lead to fatigue problems. Conventional fastener assemblies may allow workpiece components to move relative to one another, which may result in fretting, excessive stresses at the interfaces of the hole and the bolt, vibrations, and the like. In aerospace applications, conventional joints may thus have a relatively short in-service life. Additionally, conventional fastener assemblies may be prone to electrical arcing or spark formation if the electrical current flows through the fastener assembly, for example, due to a lightning strike.
Aircraft are often made of lightweight composite structures that are unable to withstand electrical currents as well as their metallic counterparts. Composite structures may be damaged by high voltage electrical currents caused by lightning strikes because composite structures do not readily conduct away the electrical currents and electromagnetic forces generated by lightning strikes. Many composite structures may have relatively poor electrical conductivity. Hence, electrical current will bypass such and pass through highly conductive materials, such as metals, if given the opportunity. Conventional metal bolt/sleeve assemblies often have gaps that lead to electrical arcing and sparks. Additionally, conventional bolt/sleeve assemblies have a tendency to cause damage in composite laminates when tolerances stack up to make relatively high interferences. Furthermore, an installed bolt typically cannot be removed without damaging the workpiece because of the high interferences. It may therefore be difficult to perform inspections or routine maintenance on joints with these types of bolt/sleeve assemblies.